1. Field of the Invention
The present invention relates to an optical recording medium that performs the recording and reproducing of signals by the irradiation of light, a driving apparatus and a driving method for the recording and reproducing thereof.
2. Description of the Related Art
As an optical recording medium that performs the recording and reproducing of signals by the irradiation of light, for example, so-called optical discs such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray Disc: trade mark) are widely used.
In regard to the current conditions regarding an optical recording medium that should take a major role in the next generation of widely-used optical recording mediums such as CD, DVD, BD or the like, firstly, the applicants suggest a so-called bulk recording type of optical recording medium as described in Japanese Unexamined Patent Application Publication Nos. 2008-135144 and 2008-176902.
Herein, the bulk recording is a technique that achieves a large recording capacity by sequentially changing focal positions and performing laser light irradiation, to thereby perform multi-layer recording in a bulk layer 102, with respect to an optical recording medium having at least a cover layer 101 and the bulk layer 102, for example, as shown in FIG. 12.
In regard to the bulk recording, in Japanese Unexamined Patent Application Publication No. 2008-135144, a recording technique referred to as a so-called micro hologram mode is disclosed.
As shown in FIGS. 13A and 13B, the micro hologram mode is classified broadly into a positive type micro hologram mode and a negative type micro hologram mode.
In the micro hologram mode, a so-called hologram recording material is used as a recording material of the bulk layer 102. As the hologram recording material, for example, a photopolymerization type photopolymer or the like is widely used.
As shown in FIG. 13A, the positive type micro hologram type is a method of concentrating two opposed fluxes (flux A and flux B) at the same position to form minute interference patterns (holograms), thereby setting the fluxes to be recording marks.
Furthermore, the negative type micro hologram mode shown in FIG. 13B is a method of erasing the interference patterns formed in advance by laser light irradiation, which is the opposite concept to the positive type micro hologram mode, thereby setting the erased portion to be recording marks.
FIGS. 14A and 14B are diagrams for illustrating the negative type micro hologram mode.
In the negative type micro hologram mode, before performing the recording action, as shown in FIG. 14A, an initialization processing for forming the interference pattern with respect to the bulk layer 102 is performed in advance. Specifically, as shown in the drawings, fluxes C and D are opposed and irradiated by a parallel light, thereby forming the interference patterns in the entirety of the bulk layer 102.
In this manner, after forming the interference patterns by the initialization processing in advance, as shown in FIG. 14B, information recording is performed by the formation of the erased mark. Specifically, by performing the laser light irradiation corresponding to the recording information in the state of focusing on an arbitrary layer position, information recording is performed by the erased mark.
In addition, as another bulk recording method, the applicant suggests a recording method by a void recording (hole recording) mode as disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902 as another bulk recording method.
The void recording mode is a method of performing laser light irradiation at a relatively high power, for example, with respect to the bulk layer 102 formed of the recording material such as photopolymerization type photopolymer, thereby recording the holes (voids) in the bulk layer 102. As described in Japanese Unexamined Patent Application Publication No. 2008-176902, a hole portion formed in this manner becomes a portion having a refractive index different from those of other portions in the bulk layer 102, which can raise the reflectivity of light in the boundary portion. Thus, the hole portion functions as the recording mark, whereby information recording by the formation of the hole mark is realized.
Since the void recording mode does not form the hologram, the recording can be achieved only by performing the light irradiation from one side. That is, there is no necessity to concentrate two fluxes at the same position to form the recording mark in the same manner as the case of the positive type micro hologram mode, and there is no necessity for a high degree of accuracy in position control for concentrating two fluxes at the same position.